Parveen Rehman, who was Director of the Orangi Pilot project, well known for its welfare work in the impoverished areas of Orangi town was gunned down by two men on a motorcycle and later died in hospital.
Senior police official, Aamir Farooqi said that Rehman, 50, was returning with her driver when the armed men intercepted her car and opened fire.
"She sustained several gunshot wounds and died in hospital," a doctor at the Abbasi Shaheed hospital said.
Television channels reported that Rehman in recent days had tried to resume the anti-polio campaign in some areas of Orangi and had also been campaigning against the powerful land mafia.
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The anti-polio vaccine campaign had to be suspended by the World Health Organization in some areas of the city after five health workers including four females were killed last December during the campaigning.
Meanwhile, on another bloody day in Pakistan's biggest city, seven other people were killed with a police constable Gulzar succumbing to his gunshot wounds in hospital.
Three mutilated bodies were also recovered in gunny bags from Soldier Bazar, Kharadar and Nazimabad areas.
A mutilated body of a 12-year boy was also found.